填空题.Space is a dangerous place, not only because of meteors (流星) but also because of rays from the sun and other stars. The 1 again acts as our protective blanket on earth. Various kinds of rays come through the air from outer space, but 2 quantities of radiation from the sun are screened off. As soon as men leave the atmosphere they are 3 to this radiation but their spacesuits or the walls of their spacecraft, if they are inside, do 4 a lot of radiation damage. Radiation is the greatest known danger to explorers in 5 . Doses of radiation are measured in 6 called "rems" (雷姆，辐射单位). Scientists have reason to think that a man can put up with far more radiation than this without being damaged; the figure of 60 rems has been agreed on. The trouble is that it is 7 difficult to be sure about radiation damage—a person may feel perfectly well, but the cells of his or her sex organs may be damaged, and this will not be discovered until the birth of deformed children or even grandchildren. Early space probes showed that radiation varies in different parts of space around the Earth. Missions to the moon (the Apollo flights)have had to cross the belts of high amounts of radiation. So far, no dangerous doses of radiation have been 8 , but the Apollo missions have been quite short. We simply do not know yet how men are going to get on when they spend weeks and months outside the protection of the atmosphere, working in a space laboratory or in a base on the moon. Drugs might help to 9 the damage done by radiation, but no really 10 ones have been found so. A. exposed B. space C. enormous D. atmosphere E. prevent F. units G. probably H. reported I. efficient J. enough K. extremely L. effective M. protect N. weight O. decrease